The Dark

I don't think your wasting your time writing your own hashing, its a great learning experience and, as you said, more tailored algorithms can be a lot faster than a generic stl one. That may be critical if the running time is tight.

However, during the contest you are likely to be under time pressure for yourself as well as the code, so maybe using the stl would help you concentrate on the parts of the problem than can't be so easily solved.